I. Field of the Invention
This invention relates generally to a cooking appliance and more specifically to a food rotator for use in an oven. The food rotator turns the item being prepared so that it will be uniformly exposed to infrared or microwave energy during cooking.
II. Discussion of the Prior Art
Turntables for use in an oven environment to provide more uniform cooking is an old concept. The Shaw U.S. Pat. No. 557,344 describes a turntable device having a spring motor for rotating the table and it dates back to the late 1800's. At that time, most ovens were wood or coal-fired and, as such, the heat was not evenly distributed within the oven chamber. By rotating the food while cooking, it would be more uniformly exposed to the infrared energy.
With the advent of natural gas and electric ranges, it became possible to design a burner arrangement such that the heat was uniformly distributed within the oven chamber. Hence, the need for turntables such as that shown in Shaw was obviated. However, in the late 1940's or early 1950's when microwave ovens came into vogue, it was discovered that microwaves are not uniformly distributed within the oven enclosure and, as a result, so-called "hot spots" developed whereby the cooking was not uniform throughout the article being heated. Thus, the turntable approach again came into popularity.
During the 1970's, built-in turntables were primarily found in microwave ovens of Japanese manufacture. U.S. Pat. No. 4,036,151 to Shin describes such a built-in turntable structure. U.S. manufacturers, on the other hand, attempted to solve the "hot spot" problem by finding ways to more evenly distribute microwaves throughout the oven cavity. So-called "mode stirring" devices were built into ovens. This approach has not been altogether satisfactory and many thousands of microwave ovens have been sold and are in use which do not adequately distribute the microwave energy through the oven cavity and which do not include a built-in turntable.
Various portable food rotator devices have been devised for use in microwave ovens. The Beh et al U.S. Pat. No. 4,254,319 describes a portable turntable device driven by a spring-type motor wherein all the parts comprising the motor and escapement are fabricated from a plastic that tends not to heat up when exposed to microwave energy. The device shown in the Beh et al Patent, however, has never been used on a large commercial scale primarily because of the inability of a plastic spring to store sufficient energy for rotating the turntable over a prolonged period.
The Cunningham U.S. Pat. No. 4,239,009 is another example of a prior are portable turntable design. Incorporated in this design were a standard spring motor and escapement constructed using metal parts. This design proved to be commercially impractical because when it was exposed to microwave energy, the metallic parts produced considerable arcing, sparking and over-heating.
A solution was provided to the drawbacks attendant in the device of the Cunningham Patent by our earlier invention which is described in U.S. Pat. No. 4,258,630 to Jorgensen et al. In this earlier design, the spring motor and escapement are disposed beneath a rotatable turntable and are contained within a smooth metallic shield having no sharp edges to serve as high potential discharge points. Having solved this problem, applicants' assignee, Northland Aluminum Products, Inc., has been highly successful in selling its MICRO-GO-ROUND.RTM. turntable for use in microwave ovens which do not have a built-in food rotator.
Microwave ovens for home use have a relatively small oven compartment and, as such, it is desirable that the turntable present a low profile so as not to take up room which could otherwise be used to contain the food items to be cooked. The Pomeroy et al Pat. No. 4,330,696 attempts to address this problem by relocating the drive motor assembly so that it does not fit beneath the rotatable table itself. Instead, the motor assembly is housed separately from the turntable structure and is positioned alongside the turntable rather than beneath it. The drive assembly is coupled through a suitable spur gear to cooperate with the gear teeth formed in the rim of the turntable element. The theory underlying the design described in the Pomeroy Patent is that the motor assembly is positioned in the corner of the microwave oven and, accordingly, is supposedly less obtrusive both in terms of occupying space otherwise available for food and in terms of being located in the zone of low density microwave energy. In practice, however, the positioning of the drive unit alongside the turntable interferes with the free rotation of certain food items when placed on the turntable beyond that which is dictated by the corners of the oven.
In attempting to address and solve the problems inherent in the prior art designs, we have previously developed a low height profile design wherein the motor, escapement and shielding are contained within a cavity between the base of the portable unit and the turntable itself. This design is shown in U.S. patent application Ser. No. 505,370 now U.S. Pat. No. 4,523,070. This design achieved the goal of providing a turntable having a low profile but with a drive assembly for the turntable being disposed beneath the rotatable table portion of the device. In this way, large casseroles, roasts and fowl will still fit within the oven space and will rotate freely without interference from any upward projecting drive elements of the turntable.
Several of the prior art designs include manual switch mechanisms which are used to permit or restrict the rotation of the turntable. Such switching mechanisms, however, are relatively inconvenient since they are not automatically actuated by placing or removing items to be cooked from the turntable. Instead, they must be manually and independently actuated. It can be seen, then, that it is desirous to provide a turntable having a low height profile and a drive assembly which will permit maximum use of the available space within the oven for cooking food and which includes a switching mechanism that automatically prevents the turntable from rotating when no item is upon it and permits the turntable to rotate when there is.